Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, Avenida General Norton de Matos s/n, 4450-208 Matosinhos, Portugal; Institute of Biomedical Sciences Abel Salazar, University of Porto, Rua de Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal; Faculty of Sciences, University of Porto, Rua do Campo Alegre 790, 4150-171 Porto, Portugal.
Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, Avenida General Norton de Matos s/n, 4450-208 Matosinhos, Portugal.
Sci Total Environ. 2017 Mar 1;581-582:359-368. doi: 10.1016/j.scitotenv.2016.12.141. Epub 2017 Jan 6.
Fluoroquinolones and cephalosporins are two classes of veterinary antibiotics arising as pollutants of emerging concern. In this work, the microbial degradation of two representative antibiotics of both these classes, enrofloxacin (ENR) and ceftiofur (CEF), is reported. Biodegradation of the target antibiotics was investigated by supplementing the culture medium with ENR and CEF, individually and in mixture. Microbial inocula were obtained from rhizosphere sediments of plants derived from experimental constructed wetlands designed for the treatment of livestock wastewaters contaminated with trace amounts of these antibiotics. Selected microbial inocula were acclimated during a period of 5months, where the antibiotics were supplemented every three weeks at the concentration of 1mgL, using acetate as a co-substrate. After this period, the acclimated consortia were investigated for their capacity to biodegrade 2 and 3mgL of ENR and CEF. Complete removal of CEF from the inoculated culture medium was always observed within 21days, independently of its concentration or the concomitant presence of ENR. Biodegradation of ENR decreased with the increase in its concentration in the culture medium, with defluorination percentages decreasing from ca. 65 to 4%. Ciprofloxacin and norfloxacin were detected as biodegradation intermediates of ENR in the microbial cultures supplemented with this antibiotic, indicating that defluorination of at least part of ENR in these cultures is not an immediate catabolic step. Abiotic mechanisms showed high influence in the removal of CEF, affecting less ENR degradation. The acclimation process with the target antibiotics led to significant shifts in the structure and diversity of the microbial communities, predominantly selecting microorganisms belonging to the phyla Proteobacteria (e.g. Achromobacter, Variovorax and Stenotrophomonas genera) and Bacteroidetes (e.g. Dysgonomonas, Flavobacterium and Chryseobacterium genera). The results presented in this study indicate that biodegradation can be an important mechanism for the environmental removal of the tested compounds.
氟喹诺酮类和头孢菌素类是两类作为新兴关注污染物的兽用抗生素。本工作报道了这两类抗生素的两种代表性抗生素恩诺沙星（ENR）和头孢噻呋（CEF）的微生物降解。通过在培养基中单独和混合添加 ENR 和 CEF 来研究目标抗生素的生物降解。微生物接种物是从用于处理受痕量这些抗生素污染的牲畜废水的实验性人工湿地植物的根际沉积物中获得的。选择的微生物接种物在 5 个月的时间内进行驯化，每隔三周在浓度为 1mgL 的条件下补充抗生素，使用乙酸盐作为共底物。经过这段时间，用 2 和 3mgL 的 ENR 和 CEF 驯化后的混合菌群来研究它们的生物降解能力。无论 CEF 的浓度如何，或同时存在 ENR，CEF 总是能在 21 天内从接种培养基中完全去除。ENR 在培养基中的浓度增加，其生物降解率下降，脱氟率从约 65%下降到 4%。在添加该抗生素的微生物培养物中检测到环丙沙星和诺氟沙星作为 ENR 的生物降解中间体，表明这些培养物中至少部分 ENR 的脱氟不是直接的代谢步骤。非生物机制对 CEF 的去除有很大的影响，对 ENR 降解的影响较小。用目标抗生素进行驯化过程导致微生物群落的结构和多样性发生显著变化，主要选择属于变形菌门（如不动杆菌属、鞘氨醇单胞菌属和寡养单胞菌属）和拟杆菌门（如食酸菌属、黄杆菌属和色杆菌属）的微生物。本研究结果表明，生物降解可能是环境去除测试化合物的重要机制。
